This invention provides over-all means for circulation of molten metals under a substantially constant head of pressure and flow rate in a substantially laminar flow downstream of the egress of the pump which is adapted for use submerged in a melting/holding furnace.
It further provides a control means for direction of a selected one of two downstream egress channels with molten metal by means of combination of the molten metal pump in downstream co-operation with a downstream flow selector means for said selection of any one of the said two channel means, said flow selector means preferably integral with the single output orifice of the molten metal pump.
The selector means may also be operated independently physically as a separated unit downstream of a prior art pump or a gravity fed source of molten metal characterized by having a constant pressure head and flow rate as might originate from molten flow into a tundish placed in a holding furnace on an upper foundry floor, without integral connection with a pump, the latter operations are not often feasible and limit foundry flexibility in moving molten metal from one furnace to another, or from one furnace to two or more separated downstream operations.
By means of the preferred combination, one may feed a single metal flow sequentially to one of two or more operations. Metal may be sequentially cast, for example, from a molten supply into various downstream operations producing solid metal, forms such as ingots, sheets, foils, tubes or rods, etc., by use of one unit fluidic control or a plurality of said unit controls in series, if desired.
Both soluble and insoluble gross solids including fluxes, slag, unmelted metals including iron, silicon, etc., firebrick refractory fragments, aluminum oxide occlusions, etc., which can damage the downstream volute pumps accumulate upon normal handling of molten metal in refractory furnaces and tend to collect upon and after formation in melting and holding furnaces. As the foregoing particulate impurities native to handling molten zinc are inherently lighter and tend to float, they tend to be drawn into top fed impeller pumps. Hence, for handling molten zinc bottom fed pumps are normally selected. On the other hand, with molten aluminum and its alloys, occluded impurities are most often heavier than the melt and tend to agglomerate and settle. Liquid aluminum metal fed into bottom-fed volute-impeller pumps have been generally avoided.
The prior art has suggested multiple specialized molten metal pump assemblies by use of alternative pump elements, including drive shafts, pump impellers as illustrative. Shorter drive shafts have been used where top feed of molten aluminum metal to a top fed impeller pump is desired. If metallic zinc was to be handled, a longer drive pump shaft and co-related inverted cup impeller fed from a bottom ingress pump was assembled. Pump assemblies have been so designed as to provide bottom fed molten metal pumps. See Sweeney et al., U.S. Pat. No. 3,048,384.
One prior art solution has proposed a system of rotary baffles, referred to as "deflector disks", driven on the same vertical drive main pump shaft provided controlled circumferential clearance of molten metal from the melting furnace by adjustment of the disk clearance on the common drive shaft both above and below annular top and bottom fed single pump ingress means. See Sweeney et al., U.S. Pat. No. 3,291,473.
Here, a volute pump has been described to be useful to pump molten metal inwardly through a single pump ingress means fed from the top. However, a single pump impeller devoid of volute means is employed.
It should also be noted that in the top and bottom entry modifications, patentee does not use a volute pump and the utility does not permit the higher temperatures essential in handling molten metals and is intended for generally lower temperature melting point chemicals. In either case, entry is through and past rotary, driven, deflector disks slightly upstream of the metal flow entry into the pump.
It is well known, however, that similar rotary power driven disks spinning within an enclosed clearance provide high shear dispersive forces. The high shear rate produced effects unwanted dispersion of foreign matter as referred to above which contaminates the melt stream. Rotary dispersion action of the described classifiers tends to defeat the filtration intended and to break up and disperse insoluble solid matter.
Here, dual volute pumps operating from a single shaft separately receive influx of molten metal which first is filtered of all suspended solids in the melt by an upper and lower restricted ingress zone completely about the periphery of the submersible pump which insures that the pump clearances are not unduly worn or damaged by entry of any one of the foregoing unmelted accumulated particulates.
One principal advance over the prior art herein disclosed is embodied in the moving parts free, selective fluidics flow control means, particularly when operated in conjunction with the dual ingress dual volute pump, both of which are more fully described herein.
The liquid metal flow upon egress from the pump and entering the downstream transition control means is controllably diverted into a selected one of two divergent controlled downstream conduits or channels without interference with over-all through-put flow rate.
Commonly the principal control of molten metal flow egressing the pump has been solely through control of the pump operation. The limitation has been primarily an on-off; flow or no-flow; operation where the driving motor means control of resultant metal flow through the pump is not instantly responsive to the "on-off" signals.
When an "on-off" flow control is employed in a moving stream of metal, particularly, a "water hammer" develops which is detrimental to the pump function and may cause breakage of the graphite parts required in the pump manufacture.
This invention makes possible downstream selection of alternative melting and holding furnaces and re-circulation within and between such furnaces and alternative delivery of a single stream of molten metal to one of two pre-selected downstream operations.
The fluidics devices of this invention can be used in tandem in plural number, if desired, making continuous operation from a single melting furnace, or a plurality of melting or holding furnaces feeding a series of varying downstream operations electively and sequentially.